1. Field of the Invention
The present invention relates to a process and apparatus for the production of liquid carbon dioxide and, in a most preferred form, permits the trigeneration of electricity, heat and liquid carbon dioxide.
2. Description of the Prior Art
U.S. Pat. No. 4,942,734 relates to a process where methane-rich fuel is combusted in a gas turbine (internal combustion heat engine). Additional methane-rich fuel is injected into the exhaust stream resulting from the combustion step to fire a steam boiler which produces steam to turn a steam turbine (external combustion heat engine), the gas turbine and the steam turbine being directly connected to an electric generator. In accordance with the present invention, any heat engine may be used, and the same can be internally or externally fired by any fuel and directly connected to either an electric generator or any other mechanical device that can do work, such as a compressor. The subject patent relates to the cogeneration of electricity and liquid carbon dioxide, whereas in accordance with the present invention the trigeneration of electricity, heat and liquid carbon dioxide is achieved. While the subject patent uses an amine solvent absorption column selective for carbon dioxide and a stripper column to remove carbon dioxide from flue gas, in accordance with the present invention it is most preferred to use a gas permeable membrane which is selective for carbon dioxide to remove carbon dioxide from the process stream. The subject patent involves the use of an ammonia absorption refrigeration cycle to liquefy compressed and dried carbon dioxide in a carbon dioxide condenser. In accordance with the present invention, an expansion turbine is used to extract work from a high-pressure residual nitrogen-rich process stream which is preferably generated in the membrane separator above mentioned. The process of the present invention also involves a recuperative heat exchange between the resultant expanded low temperature residual nitrogen-rich stream and a compressed and dried carbon dioxide-rich permeate stream in a carbon dioxide condenser. In accordance with the present invention, either an absorption or vapor-compression refrigeration cycle can also be used to liquefy compressed and dried carbon dioxide in a carbon dioxide condenser.
U.S. Pat. No. 5,001,902 relates to the cogeneration of electricity and liquid carbon dioxide whereas the process of the present invention permits the trigeneration of electricity, heat and liquid carbon dioxide. The subject patent involves the use of a vaporizable liquid fuel, particularly alcohols and hydrocarbons, fired in a flameless porous fiber burner with low NOX production which is used to make high pressure steam in a boiler which turns a steam turbine which drives an electric generator. In accordance with the process of the present invention, any heat engine, internally or externally fired by any fuel, can be directly connected to either an electric generator or any other mechanical device that can do work, such as compressor, for example, although it is preferred in accordance with the present invention to use a natural gas or methane fired internal combustion engine connected directly to an electric generator. The subject patent requires that liquid fuel be vaporized by injection into combustion air preheated by heat exchange with a burner flue gas. Fuel pre-treatment is not needed in the present invention. The subject patent involves the use of an amine solvent absorption column for the recovery of carbon dioxide from flue gas supplied by a flue gas blower and a stripper column with a reboiler heated by steam from an intermediate pressure stage of the steam turbine. It is most preferred in accordance with the present invention to use a gas-permeable membrane which is selective for carbon dioxide to remove carbon dioxide from a process stream. The subject patent specifies liquefication of carbon dioxide in an unspecified system; the process of the present invention involves a very specific procedure for liquefication of carbon dioxide.
U.S. Pat. No. 5,025,631 relates to the cogeneration of electricity and refrigeration with low NOX. The process of the present invention enables the trigeneration of electricity, heat, and liquid carbon dioxide. The subject patent involves the use of a gaseous fuel which is preheated at high pressure by a heat exchange with hot flue gas in a pre-heater. The high-pressure fuel gas is then expanded in a turbo-expander (expansion turbine) which drives a centrifugal compressor for the refrigerant vapor of a refrigeration system. The process of the present invention does not require any fuel pretreatment. The subject patent discloses expanded fuel gases admixed with a limited amount of air and then fired in a flameless porous fiber burner with low NOX production and other pollutants which is used to make high-pressure steam in a boiler which turns a steam turbine that drives an electric generator. In accordance with the process of the present invention, any heat engine, internally or externally fired by any fuel and directly connected to either an electrical generator or any other mechanical device that can do work, such as a compressor, for example, can be used. It is preferred in the present invention to use a natural gas or methane-fired internal combustion engine connected directly to an electric generator.